The invention relates to a component of a fluid-flow machine, essentially comprising a flow-deflecting device which is connected in a root region to a platform, the penetration of the flow-deflecting device with the platform being provided by a pressure-side profile line, a suction-side profile line, and a leading edge base point and a trailing edge base point, and the top view of the platform essentially exhibiting the shape of a parallelogram on which there is arranged a nose running in the circumferential direction.
The blades of modern gas turbines are subjected to high mechanical loads because of centrifugal forces, aerodynamic forces and thermal stresses. Subjected in particular to extremely high loads is the blade transition, that is to say the region in which the actual flow-deflecting devices merge into the platforms. The entire torque induced by aerodynamic forces must be transmitted at this point, and in the case of blades their centrifugal load also has to be withstood. In the case of high hot-gas temperatures and, in particular, when the components are being cooled, it is precisely in the region of the transition from the blade to the platform that high temperature gradients continue to have to be taken into account.
In top view, such platforms of blades are mostly presented as parallelograms of which two sides are orientated in the circumferential direction of the machine, while the two other sides run approximately in the direction of the mean flow angle. A nose running in the circumferential direction is mostly arranged at an end situated downstream. In the installed state, the noses of a platform respectively engage in a corresponding cutout in another component, and thereby seal the interspace of the platforms in the flow direction.
The penetration line of the blade, which is essentially to be characterized by a suction-side and pressure-side profile line as well as a trailing edge base point and a leading edge base point, is situated inside the surface thus described. On their underside, the platforms bear devices for the purpose of anchoring the components in the housing or on the shaft, and therefore constitute a very solid and thus also stiff structure.
From the top view of the configuration thus described the person skilled in the art recognizes in the transition from the flow-deflecting device to the platform the basic features of a three-point bearing which transmits the torque induced by aerodynamic forces into the platform. The bearing points are in this case the base points of the trailing edge and leading edge, and the suction-side profile line in the region of the maximum curvature.
The introduction of the forces and torques into the stiff platform produces complex three-dimensional states of stress at the said points. Because of the stiffness of the platform, the material cannot compensate the stresses by elastic strains; the abovementioned temperature gradients cause differential strains which likewise cannot take place freely because of the component geometry, and this further increases the loading of the component.
Furthermore, relatively narrow radii must be provided in the transition from the platform to the flow-deflecting device. The result of this is a notch effect and an unfavourable force flux in this region.
Thus, overall strong stresses are induced in a zone in which the material strain is extremely impeded. In particular, when the strength of the material is reduced in any case by high temperatures, the peak stresses occurring limit the service life of a component.
The invention aims to provide a remedy here. In the case of a component of a fluid-flow machine, essentially comprising a flow-deflecting device which is connected in a root region to a platform, the penetration of the flow-deflecting device with the platform being provided by a pressure-side profile line, a suction-side profile line, and a leading edge base point and a trailing edge base point, and the top view of the platform essentially exhibiting the shape of a parallelogram on which there is arranged a nose running in the circumferential direction, it is the object of the invention to configure the transition from the platform to the flow-deflecting device in such a way that the excessive stresses mentioned in the introduction are avoided as far as possible. In particular, the contour of the component is to be appropriately shaped in the region of the transition from the platform to the flow-deflecting device.
According to the invention, this is achieved, on the one hand, by virtue of the fact that the trailing edge base point of the flow-deflecting device is situated in a corner of the parallelogram.
It is likewise possible within the scope of the invention for the leading edge base point of the flow-deflecting device to be situated in a corner of the parallelogram or, for a long side of the parallelogram to be arranged as a tangent to the suction-side profile line. All three features can be intercombined as desired.
In particular, in conjunction with the placing of the trailing edge base point, it is advantageous when the nose of the platform is arranged at the downstream end of the suction-side long side of the parallelogram of the platform.